First-principles molecular dynamics simulations in the canonical ensemble at temperatures of 333 and 363 K and at the corresponding experimental densities are carried out to investigate the behavior ...of the 1:2 choline chloride/urea (reline) deep eutectic solvent and its equimolar mixture with water. Analysis of atom–atom radial and spatial distribution functions and of the H-bond network reveals the microheterogeneous structure of these complex liquid mixtures. In neat reline, the structure is governed by strong H-bonds of the trans- and cis-H atoms of urea to the chloride ion. In hydrous reline, water competes for the anions, and the H atoms of urea have similar propensities to bond to the chloride ions and the O atoms of urea and water. The vibrational spectra exhibit relatively broad peaks reflecting the heterogeneity of the environment. Although the 100 ps trajectories allow only for a qualitative assessment of transport properties, the simulations indicate that water is more mobile than the other species and its addition also fosters faster motion of urea.
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Hydrophobic deep eutectic solvents (DESs) are a new generation of water immiscible solvents that have been presented in the literature for the first time in 2015. These solvents have been used for ...many applications. Here, an overview is given regarding hydrophobic DESs with their physicochemical properties, applications, and the challenges and limitations that the field currently is experiencing. First, a general introduction and an introduction to hydrophobic DESs are presented to explain more about DESs, their origin, and hydrophobic ones. Here, also, an overview of all the hydrophobic DESs presented in the literature is given. After the introduction, physicochemical properties such as density, viscosity, melting point, degradation temperature, volatilities, and solvatochromic properties are discussed. It is continued with the discussion of 21 different applications of hydrophobic DESs. In general, applications related to liquid–liquid extractions, liquid–liquid microextractions, formation of two and three phase systems, removal of components from leaves, gas–liquid extractions, formation of hydrogels, membrane formation, centrifugal partition chromatography, formation of a ferrofluid, coating, photoluminescence, and dye-sensitized solar cells, and catalysis have been investigated. Finally, challenges and limitations of hydrophobic DESs are discussed.
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The liquid–liquid extraction of a nitrogen-containing aromatic “pyridine” and nitrogen/sulfur-containing aromatic “benzothiazole” from n-hexane and n-heptane using deep eutectic solvents (DESs) was ...studied in this work. A DES composed of methyltriphenylphosphonium bromide as hydrogen bond acceptor and ethylene glycol as hydrogen bond donor was selected for this separation. The main objective of this work was to assess whether the same DES can be applied for the denitrogenation “extraction of pyridine” and desulfurization “extraction of benzothiazole” of fuels. Moreover, the influence of n-alkane chain length on the extraction performance was studied. First, the solubilities of the pyridine, benzothiazole, n-hexane, and n-heptane in the DES were determined at 298.2 K and 1.01 bar. Thereafter, the pseudoternary liquid–liquid equilibrium (LLE) data for the four systems {n-hexane + pyridine + DES}, {n-heptane + pyridine + DES}, {n-hexane + benzothiazole + DES}, and {n-heptane + benzothiazole + DES} were determined at a temperature of 298.2 K and a pressure of 1.01 bar. The assumption of a pseudoternary system was validated showing that none of the DES’ constituents appears in the raffinate phase. From the LLE data the distribution ratios and selectivites of pyridine and benzothiazole were calculated. Both pyridine and benzothiazole were successfully extracted from their mixtures with n-hexane and n-heptane, with pyridine showing higher selectivity than benzothiazole and almost similar distribution ratios. Finally, The LLE data were correlated with the nonrandom two-liquid model using ASPEN PLUS. The modeled results showed a strong correlation with the experimental results (relative mean standard deviation (%)) = 0.04–0.36).
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In an attempt to develop an alternative process that meets the criteria of “green” and economically sound technology in fuel purification, simultaneous extractive desulfurization, denitrification, ...and dearomatization using natural deep eutectic solvents (NADESs) were investigated. A NADES composed of betaine (Bet) as a hydrogen bond acceptor (HBA) and levulinic acid (LevA) as a hydrogen bond donor (HBD) was investigated for its extraction capacity of thiophene, pyridine, and toluene from n-decane via liquid–liquid extraction. First, the HBA/HBD molar ratio was optimized based on the highest overall extraction efficiency, which was achieved for Bet/LevA (1:7). Furthermore, the selected NADES was characterized by measuring its density, dynamic viscosity, and water content. Then, the solubility of each fuel impurity in the NADES was measured. Moreover, the liquid–liquid equilibrium (LLE) data of the pseudo-ternary systems {n-decane (1) + thiophene/pyridine/toluene (2) + Bet/LevA (1:7) (3)} were determined at 298.15 K and 1.01 bar. The assumption of a pseudo-ternary system, which means that the NADES stays intact in one phase, was validated experimentally. The solute distribution ratios, selectivities, and the extraction efficiencies of each impurity at a 1:1 solvent-to-feed mass ratio were calculated from the experimental LLE data and compared to a benchmark solvent (i.e. sulfolane) and other ionic liquids and DESs reported in the literature. The LLE data were also correlated using the nonrandom two-liquid thermodynamic model. The regressed LLE data showed good agreement with the experimental data as the root-mean-square deviation was found to be ≤0.29%. Finally, it is clear that Bet/LevA (1:7) can be considered as a potential natural solvent for combined desulfurization, denitrification, and dearomatization processes.
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In a previous work, we proved that the deep eutectic solvents (DESs) consisting of mixtures of tetraalkylammonium salts with polyols are promising candidates for oil desulfurization based on the ...obtained liquid–liquid equilibrium (LLE) data. In this study, the capability of DESs containing other salts (e.g., different alkyl chain lengths or different functional groups on the ammonium cation) for the extraction of thiophene from {n-hexane + thiophene} mixtures via LLE was evaluated. Therefore, four DESs composed of tetraethylammonium chloride or methyltriphenylphosphonium bromide as hydrogen bond acceptors and ethylene glycol or glycerol as hydrogen bond donors were prepared. Thereafter, the binary solubilities of the aliphatic hydrocarbon (n-hexane) and the thiophene in DESs were measured at 298.2 K and atmospheric pressure. Next, ternary liquid–liquid equilibrium (LLE) data for the four ternary systems {n-hexane + thiophene + DES} were measured at 298.2 K and atmospheric pressure. The conductor-like screening model for real solvents (COSMO-RS) was used to better understand the extraction mechanism of thiophene. Experimentally obtained solute distribution coefficients and selectivities were calculated and compared to relevant literature. All DESs were found to be good candidates for extractive desulfurization with higher selectivities but somewhat lower distribution coefficients as compared to conventional ionic liquids. It was found that longer alkyl chain lengths on the cation yield higher distribution coefficients but lower selectivities, and the replacement of an alkyl group by a phenyl group on the cation generally yields lower distribution ratios ratios but higher selectivities.
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•Separation of S–, N–, and aromatics from fuels using acidic deep eutectic solvents.•Diesel model consisted of toluene, thiophene, pyridine, and pyrrole in n-decane.•Single-stage, ...multi-stage, and multi-cycle extraction of the diesel were evaluated.•Distribution ratios and selectivities were determined and compared to literature.•The LLE data has been successfully correlated using the NRTL model.
Based on the literature, deep eutectic solvents (DESs) have been proven to be promising candidates for the separation of aromatics or heteroaromatics (“sulfur-/nitrogen- containing aromatics”) from fuels. However, most studies investigated the separation of a single fuel impurity (aromatics or heteroaromatics) from n-alkanes. Thus, to realistically represent a process that simulates the treatment of both types of aromatics, this work investigated the application of DESs in simultaneous dearomatization, desulfurization, and denitrogenation of fuels, particularly “diesel” using an arbitrary fuel model consisting of {5 wt% toluene + 5 wt% thiophene + 5 wt% pyridine + 5 wt% pyrrole + 80 wt% n-decane}. The selected DES was comprised of tetrapropylammonium bromide and acetic acid at a 1:4 M ratio. The DES performance was evaluated based on single-stage liquid–liquid extraction, the Liquid-Liquid Equilibrium (LLE) data of each impurity, multi-stage, and multi-cycle extraction of the diesel model. Furthermore, the influence of initial concentration and mixing effects of impurities were also studied. The results showed that complete removal of pyrrole and pyridine (“≈100%”) can be achieved in 2 stages only, while extraction efficiencies of 68% and 89% for toluene and thiophene, respectively, were achieved after the 5th stage. Based on the obtained results, it was concluded that acidic DESs could be considered as potential solvents for the simultaneous dearomatization, desulfurization, and denitrogenation of diesel fuels.
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Industrially, deep dearomatization of oil fuels is achieved via catalytic hydrodearomatization (HDA). However, this process suffers from several drawbacks. The most pronounced disadvantages are the ...intensive energy consumption and the low efficiency toward some aromatic species. With the aim of lowering energy consumption as well as improving the removal efficiency of this process, selective liquid–liquid extraction was proposed in this work. A phosphonium-based deep eutectic solvent (DES) composed of methyltriphenylphosphonium bromide (MTPPBr) and triethylene glycol (TEG) in a molar ratio equal to 1:4 (MTPPBr/TEG) was selected for this investigation. The DES was characterized by its water content, density, viscosity, and degradation temperature. Toluene, thiophene, and quinoline were selected to represent the aromatic species in the oil. However, the oil fuel was represented by n-heptane. Next, the solubility of toluene, thiophene, quinoline, and n-heptane in the pure TEG and MTPPBr/TEG was measured at 298.2 K and 1.01 bar. To assess the selectivities and the solute distribution coefficients of the DES for each compound, liquid–liquid equilibrium (LLE) data for the systems {toluene + n-heptane + MTPPBr/TEG}, {thiophene + n-heptane + MTPPBr/TEG}, and {quinoline + n-heptane + MTPPBr/TEG} were reported at 298.2 K and 1.01 bar. Afterward, a parametric study on an arbitrary oil model of {20% toluene + 2% thiophene + 2% quinoline + 76% n-heptane} was conducted by first testing the single-stage liquid–liquid extraction efficiency for each impurity “toluene, thiophene, and quinoline” at 298.2 K and 1.01 bar. Then, the effects of various operating parameters including the extraction temperature, the solvent-to-feed ratio (S/F), and the initial concentration of the impurity were investigated. Moreover, the number of extraction stages was estimated. Finally, the effect of the repetitive use of DES as well as the possibility of DES regeneration was studied.
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Mercury capture is a major challenge in petroleum and natural gas processing. Recently, ionic liquids (ILs) have been introduced as mercury extractants from oil and gas. ILs yield very high mercury ...extraction efficiencies (>95%) from hydrocarbons, but their drawbacks include complex synthesis, toxicity, and difficult regeneration after mercury capture. In this work, a new technology using deep eutectic solvents (DESs) for elemental mercury (Hg0) extraction from hydrocarbons is demonstrated. DESs are an innovative class of designer solvents exhibiting similar properties as ILs, such as low vapor pressure and low flammability, but DESs are formed from inexpensive hydrogen-bond donor and acceptor compounds that are often biodegradable. In this work, four DESs were investigated including choline chloride:urea, choline chloride:ethylene glycol, choline chloride:levulinic acid, and betaine:levulinic acid, where the molar ratio is 1:2 in all cases. The DESs were tested for their thermal stability, density, and viscosity. Their performance for mercury extraction was assessed using saturated solutions in n-dodecane as the model oil. It was found that solvent to feed ratios of 1:1 and 2:1 at temperatures of 303.15 and 333.15 K and atmospheric pressure yield extraction efficiencies greater than 80% for all four DESs. First-principles molecular dynamics simulations probing the solvation in choline chloride:urea indicate a tight first coordination shell for mercury. Calculation of the Hg–Hg potential of mean force supports formation of a mercury–mercury polycation for a pair of Hg1+ ions, but not for pairs of Hg0 and Hg2+ species. Geometric analysis of the speciation and Mulliken population analysis support a redox reaction involving Hg2+ + 2Cl–.
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In our previous work, we showed that phosphonium-based deep eutectic solvents (DESs) are good candidates for the extractive denitrogenation of oil fuels. In particular, pyridine was successfully ...extracted from n-hexane and n-heptane via liquid-liquid extraction. The extraction using ‘methyltriphenylphosphonium bromide and ethylene glycol’ DES yielded high distribution ratios and selectivities of pyridine. In this work, two phosphonium-based DESs were prepared, the first one was a “binary DES” composed of methyltriphenylphosphonium bromide and glycerol and the second one was a “ternary DES” composed of methyltriphenylphosphonium bromide, glycerol, and ethylene glycol. One objective was to assess the extraction properties of the DESs for pyridine from n-alkanes. Another objective of this work was to study the influence of n-alkane chain length on the extraction performance. Thus, the oil models selected were n-hexane/pyridine, n-heptane/pyridine, and n-octane/pyridine. First, the prepared DESs were characterized for their water content, density, viscosity, and the degradation temperatures. Then the solubility of n-hexane, n-heptane, n-octane, and pyridine in the DESs was measured at 298.2 K and 1.01 bar. Afterward, the liquid-liquid equilibrium (LLE) data of the pseudo-ternary systems {n-alkane + pyridine + DES} were determined at a temperature of 298.2 K and a pressure of 1.01 bar. The consideration of a pseudo-ternary system was validated by showing that none of the DES constituents appears in the n-alkane-rich phase “the raffinate”.
The solute distribution ratios and the selectivities were calculated from the experimental LLE data and compared to our previous work and some relevant literature. Furthermore, the LLE data were correlated with the non-random two-liquid (NRTL) model using ASPEN Plus. There was good agreement between the calculated experimental results. Finally, the COnductor like Screening MOdel for Real Solvents (COSMO-RS) model was used to predict the ternary tie lines for the studied systems. Based on the good distribution ratios and selectivities obtained, the studied DESs can be considered as potential solvents for extractive denitrogenation processes.
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The reduction of the sulfur content in crude oil is of utmost importance in order to meet the stringent environmental regulations. Thiophene and its derivatives are considered key substances to be ...separated from the crude oil. In previous works, six deep eutectic solvents (DESs) based on tetraethylammonium chloride, tetrahexylammonium bromide and methyltriphenylphosphonium bromide as hydrogen bond acceptors (HBAs) and polyols (ethylene glycol and glycerol) as hydrogen bond donors (HBDs) were successfully applied for the extraction of thiophene from {n-alkane + thiophene} mixtures via liquid-liquid extraction. One of the objectives of this work was to study the effect of the aliphatic hydrocarbon type/length (e.g. n-hexane vs n-octane) on the extraction performance of the same DESs. Extraction performance was evaluated by the selectivity and the thiophene distribution coefficient. Based on new experimental data, higher selectivities and lower thiophene distribution coefficients were obtained when thiophene was extracted from n-octane instead of n-hexane. Another objective was to predict the phase behavior of the ternary systems {n-alkane + thiophene + DES} using Perturbed-Chain Statistical Associating Fluid Theory (PC-SAFT). The PC-SAFT “pseudo-pure component” approach was applied, in which a DES was considered as a pseudo-pure compound (not a mixture). The pure-component parameters of the DESs were obtained by fitting to liquid density data, which were measured at temperatures between 298.2 K and 323.2 K. Binary interaction parameters were fitted to experimental binary LLE data for the systems {n-alkane + DES} and {thiophene + DES} at 298.2 K and atmospheric pressure, while the LLE data of the ternary systems {n-alkane + thiophene + DES} were fully predicted. It was found that the distribution coefficients and selectivity of the ternary systems containing DESs could be qualitatively well predicted using this model.
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